<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    <div id="app"></div>
        <script src="https://unpkg.com/vue/dist/vue.min.js"></script>
        <script>
            var app = new Vue({
                el:'#app',
                data:{
                    a:2
                },

                created:function(){
                    document.write(this.a)     //输出a的值
                },

                mounted:function(){
                    console.log(this.$el);
                }
            })
        </script>
</body>
</html>